A photoconductive drum has, on the surface thereof, a photosemiconductor layer on which an electrostatic latent image is formed. Static electricity on the photoconductive drum is grounded via drum flanges press-fit in both ends of the drum.
For one photoconductive drum, the drum flanges are used in two places at both the ends.
Unnecessary charges are grounded via at least one of the drum flanges. Usually, a metal shaft for grounding is inserted into the drum flange used for the grounding.
A coupling is provided in the metal shaft. The coupling has a coupling projection. A coupling recess is provided in the center of the drum flange. The coupling recess fits with the coupling projection.
A coupling structure is formed by the coupling recess and the coupling projection. The photoconductive drum rotates according to the transmission of driving force from the coupling projection to the coupling recess.
Alternatively, as another coupling structure for transmitting the driving force, a structure in which a gear provided in an outer circumference of the drum flange is meshed with another gear may be used. The photoconductive drum rotates according to the transmission of the driving force via the two gears.
The drum flange grounds charges of the photoconductive drum. The drum flange is obtained by 1/ combining a sheet metal with a structure molded from a nonconductive material such as resin or 2/ being molded from a conductive material.
A charging roller and a transfer roller impart charges to a photoconductive member. In an apparatus including the charging roller and the transfer roller, the drum flange of 1/ above is used. Driving force is transmitted to the charging roller and the transfer roller by the gear of the nonconductive resin provided in the outer circumference of the drum flange.
High bias voltage is applied to the charging roller and the transfer roller. A distance for insulation along surfaces is required to be secured between the charging roller and the photoconductive drum. The distance for insulation is required to be secured between the transfer roller and the photoconductive drum as well.
In the past, there is proposed a charge removing device that makes it possible to prevent a leak of an electric current from a conductive core of a charge removing roller to a photoconductive member (JP-A-06-3924).
JP-A-06-3924 discloses a technique for providing insulating members in rings of the conductive core and the photoconductive member and securing a distance along surfaces between the conductive core and the photoconductive member.
There is also proposed an image forming apparatus that makes it possible to prevent a leak due to a distance along surfaces (JP-06-51656).
JP-06-51656 discloses a technique for increasing the distance along the surfaces by forming small-diameter sections at both ends of a transfer roller and providing, in circumferential surfaces of the small-diameter sections, four grooves orthogonal to an axis of the transfer roller.
However, the drum flange of 1/ above is obtained by combining the nonconductive material having the resin gear and the sheet metal. Therefore, in the drum flange of 1/ above, it is necessary to bring a metal member into contact with the shaft in order to ground the photoconductive drum.
In the drum flange of 1/ above, it is necessary to additionally provide a grounding leaf spring and the like. In this case, the number of components further increases and the wear of the shaft is caused by the grounding leaf spring.
When the grounding drum flange of 2/ above is used, if the material of the drum flange is a metal material such as aluminum, the wear of the shaft is caused by friction of the two kinds of metal. In particular, if a gear structure is provided in the outer circumference of the drum flange, it is difficult to mold the gear.
On the other hand, if the material of the grounding drum flange of 2/ is conductive resin, there is a risk of a leak. This is because high bias voltage is applied between the photoconductive drum and the transfer roller.
If the gear structure is provided in the outer circumference of the drum flange, there is a risk that, when the driving force is transmitted from the photoconductive drum to the transfer roller, the distance for insulation along the surfaces between the drum flange and the shaft of the transfer roller is reduced.
A risk of a leak between the photoconductive drum and the charging roller is the same as the risk of the leak between the photoconductive drum and the transfer roller.
As a structure for transmitting the driving force from the photoconductive drum to the charging roller or the transfer roller, a conductive material may be used for one drum flange and a nonconductive material may be used for the other drum flange.
It is also possible to provide a gear on an outer circumferential surface of the nonconductive drum flange. In this case, one drum flange is driven for grounding of the photoconductive drum as well. The other drum flange drives the charging roller and the transfer roller.
However, if functions are divided to the respective flanges, the thicknesses of the drum flanges increase. If the two drum flanges are combined with the photoconductive drum, the total length in a longitudinal direction of the photoconductive drum increases, leading to an increase in size of the apparatus.